1. Field of the Invention
This invention relates to a mechanism for latching an optical fibre connector, and in particular a latching mechanism for a connector making optical connection between a panel or mother board and a circuit board.
2. Description of the Prior Art
It is relatively common in the electronics industry, to transfer signals by way of an optical fibre due to a number of advantages that light transmission has over transmission of electrical signals, namely the very high transmission rate of signals and the insensitivity of light signals to electrical and magnetic fields. One common example of high speed data transmission is between substrate boards with printed electrical circuits thereon, whereby it is often desirable to have both electrical and optical connection between the boards, this connection often occurring between a mother board and daughter boards.
An optical fibre cable is typically built up of an inner core surrounded by cladding, and therearound fibres for reinforcement and further, a protective plastic insulation. The core carries all or most of the light and is usually made of glass or plastic, whereby the diameter of this core may even be as small as two to eight microns. The cladding surrounding the core is typically made of plastic or glass and serves to keep the light within the inner core due to the specifically chosen, and different refraction indexes of the core and cladding, whereby the outer diameter of this cladding may be around twenty to one hundred and twenty five microns. The very small diameter of the inner, light transmitting core means that great accuracy is needed when coupling two optical fibres together. This is achieved by feeding the core and shell through the bore of a precisely manufactured ferrule and holding it therein by bonding, the optical fibre projecting through the tip of the ferrule, and the tip of the ferrule is then finely polished so that the optical fibre is flush to the tip of the ferrule. The ferrule is then inserted into a precisely manufactured sleeve which accurately centers and aligns the ferrule whereby the ferrule of another optical cable can be introduced through the other end of the sleeve until both ferrule tips butt against each other in accurate alignment. It is also important to ensure that the gap between the tips of connecting optical fibres is as small as possible and remains constant, thus requiring that the ferrules press against each other. This is achieved by springs mounted in the optical fibre connector and pushing against the ferrule. The spring also absorbs the varying axial positions of the ferrule tips. In order to allow the accurate centering of the ferrules in the sleeve, it is necessary to allow the ferrules to "float" with respect to the connector, this being achieved, for example, by leaving some play between the ferrule and the housing.
One of the difficulties of making optical connection from board to board arises from the inaccurate spacing of the boards which could be caused, for example, by using a hybrid connector where a number of adjacent optical and/or electrical connectors are positioned on a board and simultaneously plugged into mating connectors on the mother board. Electrical connectors can be easily designed for absorption of two or three millimetres of axial misalignment by simply making the receptacle and mating pin or tab terminal sufficiently long. The problem with optical connectors however, is that the axial misalignment is absorbed by the spring means as mentioned above, which may produce either a very high compression force or insufficient compression force. This varying spring force is undesirable due to the potentially high loads on the mother board and the uncontrolled butting forces of the ferrules. Additionally, it is desirable to avoid taking up the spring forces through the boards as it causes them to warp and also requires stronger and more expensive structural support thereof.
Some of the above problems have been partially overcome by the prior art described in "Compact and Self-Retentive Multi-Ferrule Optical Back Panel Connector" published in "Journal of Light Wave Technology, VOL. 10, NO. 10, October 1992". This reference describes a jack mounted to a back panel and a plug mounted to a printed circuit board for optical connection therebetween, whereby the plug has a latching mechanism for latching to an inner housing of the jack. The plug also has a latch release which disconnects the plug and jack from an outer housing of the jack, this outer housing being connected to the backpanel. This solution provides a means of releasing the connection spring forces from the boards and also allow axial movement of the plug and jack with respect to the backpanel, thereby absorbing axial tolerances. One of the problems however, associated to this solution, is that the backpanel jack may have a considerable number of optical connections, whereby the optical cables leading into the rear of the back panel jack are relatively heavy and stiff, thereby loading the jack.
The plug however must be able to slide within an outer housing meaning that the fixture between the jack and outer housing must allow a little play. Not only is the fixture of the jack to the backpanel thus weakened by the sliding requirement, but sliding of the jack within the outer housing is made more difficult due to the increased frictional force and tilting of the jack within the outer housing because of the loading from the optical cables.